You could always check That Iso site for a Leafgreen CIA, then installing it with your favourite CIA manager.
(unless you don't have CFW; in that case, you'll never get GBA games at perfect FPS on o3DS...)

I did that, but games didn't work. I got error like ''something is corrupted please hold power button to shut down console''.

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Which CFW are you using? If you're using AuReiNand, you only have to install the game to SysNAND as well as EmuNAND. If you're using something else, you have to install a patched AGB_FIRM, as well as installing the game to SysNAND.

So, I just need to download them and extract them to that location which you gave me? What after it? I should install cia and game will work?

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Oh, no, that's only if you wanted to use gpSP. Since you're on RxTools, all you need to do is find the Old 3DS Patched AGB_Firm from That Iso site. You install it to the NAND on both SysNAND and EmuNAND via switching to NAND mode in FBI by pressing L, then selecting the AGB_FIRM and installing it. Afterwards, to get any GBA game to work, you just need to install them once to SysNAND, and once to EmuNAND.
I think that covers everything...forgive me, as I'm very dumb and tend to not read everything all at once.